The present invention relates to an epoxy resin composition, which can be preferably applied to an insulating members such as an insulating support member and an insulating spacer between electric members, used for a switching device of an SF6 gas insulating device for sealing SF6 gas, an inner-gas-duct power transmitting device and other electric apparatuses.
In recent years, SF6 gas having a superior electrical insulating property has come to be used as an insulating medium for insulating devices such as transformer devices and breakers. Although the SF6 gas is chemically stable, it is decomposed by corona discharging or arc discharging generated inside the insulating device to form SF2, SF4, S2F2, SO3, SOF4, and SO2F4. Among these, SF4 reacts with water existing in the insulating device to be decomposed as shown in the following reaction formulas (1) and (2) so that HF gas is generated.
SF4+H2Oxe2x86x92SOF2+2HFxe2x80x83xe2x80x83(1)
SOF2+H2Oxe2x86x92SO2+2HFxe2x80x83xe2x80x83(2)
With respect to parts such as insulating members including an insulating member such as an insulating support member and an insulating spacer between electric members, used for a switching device of an insulating device using SF6 gas as an insulating medium, an inner-gas-duct power transmitting device and other electric apparatuses, an insulating molded article made from an epoxy resin composition has been conventionally used because it has superior insulating property, mechanical property and moldability. With respect to the filler thereof, silica (SiO2) powder is used since it has a low dielectric constant and a high mechanical strength. Therefore, the silica powder is decomposed and deteriorates as shown in the following reaction formula (3):
SiO2+4HFxe2x86x92SiF4+2H2O
As a result, the surface resistance of the insulating molded article becomes low to carry out dielectric breakdown. And as corrosion develops, its mechanical properties also deteriorate.
In order to solve this problem, for example, Japanese Unexamined Patent Publications Nos. 247449/1989 (Tokukaihei 1-247449), 130126/1992 (Tokukaihei 4-130126) and 341711/1992 (Tokukaihei 4-341711) disclose techniques, wherein aluminum oxide (alumina) powder having a resistant property (hereinafter referred to as xe2x80x9cSF6-gas resistancexe2x80x9d) to decomposed products (HF gas)generated from SF6 gas is used as the filler.
However, since the alumina powder normally has a comparatively high dielectric constant of 9 to 11, the dielectric constant of the insulating molded article containing the alumina powder also becomes high. In particular, in recent years, along with development of high-voltage, miniaturized electric apparatuses containing insulating devices, an insulating molded article that can be resistant to severer service conditions have been demanded. From the electrical viewpoint, since a reduction in the corona discharging starting voltage through modification in shape has become a major objective, it is not preferable to have a higher dielectric constant. Reduction of a filling amount of alumina powder is also suggested, but this results in degradation in the mechanical strength and cracking resistance of the insulating molded product.
As a filler having a dielectric constant lower than alumina powder and an SF6-gas resistance, examples are dolomite, sodium fluoride, aluminum fluoride, magnesium fluoride and the like. However, an insulating molded article comprising an epoxy resin composition containing these fillers fails to provide proper mechanical strength, cracking resistance, and moldability. Moreover, Japanese Examined Patent Publication No. 38718/1974 (Tokukoushou 49-38718) discloses a technique in which cordierite is used together with magnesium fluoride as a filler. But the above-mentioned problem has not still been solved.
Namely, development of an epoxy resin composition has been demanded, which has superior resistance to decomposed products (HF gas) from SF6 gas, mechanical strength and cracking resistance in a well balanced manner and can provide an insulating molded article having a low dielectric constant.
In order to solve the above-mentioned problems, the objective of the present invention is to provide an epoxy resin composition which has superior resistance to SF6 gas, mechanical strength and cracking resistance in a well balanced manner and which can provide an insulating molded article having a low dielectric constant.
The present invention relates to an epoxy resin composition for an SF6-gas insulating device, which is obtained by adding a silicate powder to an epoxy resin.
Moreover, the present invention relates to an epoxy resin composition for an SF6-gas insulating device, which is obtained by adding a silicate powder, or a silicate powder and an inorganic powder other than the silicate compound, to an epoxy resin.
In these cases, the silicate compound is preferably an independent silicate.
Moreover, the silicate compound is preferably a cyclic silicate.
Moreover, the silicate compound is preferably a linear silicate.
Furthermore, the independent silicate is preferably selected from the group consisting of forsterite, fayalite, tephroite, knebelite and monticellite that have an olivine structure.
And the independent silicate is preferably zircon.
Moreover, the cyclic silicate is preferably cordierite.
Moreover, the linear silicate is preferably wollastonite that belongs to the pyroxene group.
Furthermore, the silicate powder preferably comprises fine particles having an average particle diameter of not more than 100 xcexcm or needle-shaped substances having an average fiber diameter of not more than 100 xcexcm.
The epoxy resin composition for an SF6-gas insulating device is obtained by further adding to an epoxy resin an organic powder or fiber, which has a glass transition temperature of not less than 140xc2x0 C. and a linear expansion coefficient of not more than 40 ppm/xc2x0 C. at a temperature not more than the glass transition temperature.
The present invention also relates to an epoxy resin composition for an SF6-gas insulating device, which is obtained by adding to an epoxy resin an inorganic powder other than the silicate compound and an organic powder or fiber having a glass transition temperature of at least 140xc2x0 C. and a linear expansion coefficient of at most 40 ppm/xc2x0 C. at a temperature not more than the glass transition temperature.
In these cases, preferably the silicate compound mainly comprises MgO and SiO2.
In this case, an amount of MgO is preferably 16 to 94% by weight in the composition.
Moreover, preferably the silicate compound mainly comprises CaO and SiO2.
In this case, an amount of CaO is preferably 20 to 90% by weight in the composition.
Moreover, preferably the silicate compound mainly comprises CaO, MgO and SiO2.
In this case, a total amount of MgO and CaO component is preferably 20 to 90% by weight in the composition.
It is also possible to use a mixture obtained by mixing at least one kind selected from the group consisting of a silicate compound mainly comprising MgO and SiO2, a silicate compound mainly comprising CaO and SiO2 and a silicate compound mainly comprising CaO, MgO and SiO2.
The present invention also relates to a molded article made from the epoxy resin compound for an SF6-gas insulating device, and also relates to an SF6-gas insulating device using the molded article.